1 Field of the Invention
The present invention is directed generally to an apparatus and method for optical measurements and/or imaging of electrical potentials using an opto-electric crystal disposed immediately above a specimen.
2 Description of the Related Art
An apparatus for measuring time dependent electrical signals in microelectronic components is known from the publication by K. E. Meyer, "Two-Dimensional E-Field Mapping with Sub Pico Resolution", Springer Series in Electrophysics, volume 21 (1985) pages 46-49. The disclosed apparatus is composed of an electro-optical crystal dielectrically mirrored at one side (see in particular, FIG. 3) that is placed onto a module surface and is scanned point-by-point with a laser beam.
Stroboscopic scanning methods for optical measurements of electrical signals in integrated Ga-As circuits are known from the publication by J. L. Freemen, "Electro-Optic Sampling of Planar Digital Ga-As Integrated Circuits", Appl. Phys. Lett. 47 (10) 1985, pages 1083-1084, and K. J. Weingarten, "Direct ElectroOptic Sampling of Ga-As Integrated Circuits", Electr. Letters, Volume 21, No. 17, pages 765 thru 766.
Further optical measuring methods which exploit the electro-optic effect are described in the publication by J. A. Valdmanis, "Subpicosecond Electro-Optic Sampling: Principles and Applications", IEEE Journ. of Quantum Electronics, Volume 22, No. 1 (1986), pages 69 thru 78.
Since only the local electrical micro-fields which are built up in the region of the interconnects in accordance with the interconnect potentials and the topographical conditions are sampled in the known methods and apparatus, it is not possible to derive the potentials or voltages present at various points within the circuit from the acquired measured data without great expense. A precise knowledge of the voltage levels and their fast measurement is a critical prerequisite for checking the operation of microelectronic components.